Effectiveness of spraytopping to control glyphosate resistant annual ryegrass (Lolium rigidum Gaud.)

摘要

Since the first occurrence in 1996, there has been a slow increase in the number of populations of annual ryegrass (Lolium rigidum Gaud.) resistant to glyphosate. Australia-wide, there are now around 40 populations from a variety of situations that have been confirmed to have resistance. A major concern is how to manage these resistant populations. Seed set in annual ryegrass can be manipulated by late season application of low rates of either glyphosate or paraquat as a spraytopping or pasture topping technique. Populations of glyphosate resistant ryegrass and a control susceptible population were treated with glyphosate or paraquat at appropriate growth stages. Seed heads were collected and seed production estimated prior to seed germinability being assessed. The susceptible population was well controlled by both glyphosate and paraquat applications when compared with untreated controls. Paraquat reduced germinable seed production by over 90% for glyphosate resistant biotypes. Glyphosate did notprovide adequate levels of control in resistant biotypes. Spraytopping with glyphosate should not be undertaken on populations known or suspected to be resistant to glyphosate. The resistance mechanism that allows seedlings to survive glyphosate applications appears to also confer resistance during seed formation. Seed set in glyphosate resistant populations can be effectively controlled using late season applications of paraquat in a range of situations. Care must be taken to ensure that the treatmentis applied to ryegrass swards of uniform maturity at the appropriate growth stage.